1. Field of the Invention
This invention relates, generally, to the art of wood working. More particularly, it relates to tools for forming corners made of boards that share a common thickness, that have differing thicknesses, or where an offset of the joint line is desired.
2. Description of the Prior Art
A forty five degree (45°) lock miter router bit or shaper cutter, hereinafter also referred to sometimes as the cutter, is used to make forty five degree (45°) beveled cuts in the edges or ends of two boards that when assembled create a ninety degree (90°) joint. Contours in the cutter also create mating male and female profiles in a portion of the adjoining edges. These profiles increase gluing surfaces which results in a joint that is stronger than a straight miter. They also prevent the assembled joint from slipping along the joint line when clamped. The cutter geometry and the procedure of cutting one board in the horizontal position and the other one in the vertical position permit a single cutter to be used. Cutter height and fence position must be set precisely, however. Conventional devices and methods for making both settings are often extremely inadequate, incorrect, or so imprecise that all too often the procedure becomes one of trial and error.
The number and capabilities of prior art devices that can be used for accurate lock miter cutter setups are extremely limited. Most non-patented devices consist of nothing more than profile matching set-up blocks. These blocks are machined with a lock miter cutter after it has been properly set up, often by trial and error. The disadvantages of these blocks are that they can only be used with the specific style and size of lock miter cutter used to create them and only with boards that are exactly the same thickness as the set-up block, usually ¾″. U.S. Pat. No. 7,448,419 to Sommerfield discloses multiple router bit set-up blocks and is adjustable but it relies on matching the profile of the cutter from the same manufacturer.
Most prior art devices include standard, adjustable machinery set-up gauges that are used to adjust the bit by comparing predetermined dimensions to a known point on the cutter. They have the same disadvantages as set-up blocks. Most are two-to-one (2:1) measuring systems, proportional dividers or linear proportioners that are used primarily to find the center of the material being cut.
U.S. Pat. No. 7,260,897 discloses a device that assumes a lock miter cutter is always vertically symmetrical or that the length/depth of the matching male/female profiles are identical, or both. Such assumptions are seldom accurate.
The geometric center point of the router bit profile of all lock miter cutters, regardless of size or shape of the profile, is located at the intersection of a line coincident with the forty five degree (45°) cutting edge and the common cutting edge between the male and female profiles. No prior art device harnesses the power of this geometric fact and therefore the known devices are of limited use in making precise setups to cut standard lock miters and are of no use in making non-standard and offset lock miter setups.
Accordingly, there is a need for an improved jig for setting lock miter shaper cutters that requires no measuring devices, table of cutter dimensions, or mathematics, that requires no additional reference objects other than a machine table, fence and boards, is small, light-in-weight, has a simple fixed design with no moving parts, requires no initial nor follow-on calibration or adjustment, is designed specifically for use with lock miter cutters, and which works with almost all brands, styles, and sizes of lock miter cutters, with the possible exception of shaper cutters having cutting edges that are chords, offset from a radius by a significant amount.
There is also a need for an improved jig for setting lock miter shaper cutters that temporarily mounts directly to and is easily attached and removed from the cutter, can be easily positioned correctly, has a reference edge, also referred to as an elongate step, and a geometric center point of the router bit profile, both of which act as stops, and which guarantees precise error-free positioning of the jig.
Moreover, there is a need for a jig that, when correctly positioned on the cutter, has a geometric center point located precisely at the exact geometric center of the cutter profile, has horizontal and vertical reference lines originating at the geometric center point of the router bit profile which allow the user to easily and precisely set cutter height and fence position in relation to the geometric center of the cutter profile by visually aligning the lines, allows the user to easily make precise setups for standard lock miter joints in boards that are the same thickness, allows the user to easily make precise setups for non-standard lock miter joints in boards having different thicknesses, and allows the user to easily make setups for off-set lock miter joints.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art how the needed structure could be provided.